This invention relates to an apparatus for forming fibrous pads, from cellulose or other fibers and including all forms of superabsorbent in any fluid conveyable form, for diapers or similar other absorbent products, and more particularly, to an apparatus employing modular foraminous forming pockets which when connected end-to-end form the periphery of a rotatable drum. The modular foraminous forming pockets are associated with both a novel and unique airflow control louver system and a screen support system which provides uniform density control across the axial and lateral dimensions of the pad. By changing the cross section of the airflow control louvers or rotatable secondary louvers appended to the primary air control louvers it is possible to also modify the density and the weight of fibers per square inch of pocket area such that the amount and density of the fibers may be varied over the width and length of the pad.
Rotary forming drums have been known for a considerable time and are in wide use in the production of disposable infant and adult diaper pads, feminine hygiene pads and similar products. Typical examples of these drum formers are described in U.S. Pat. No. 4,859,388 to Peterson et al and U.S. Pat. No. 5,044,052 to Hertel et al. Typical rotary drum type pad forming systems use a fixed outer drum to which pad forming pockets are attached and radial support struts positioned under the forming wires or screens. These supports are typically spaced about 6 to 10 radial degrees apart, measured at the inside diameter of a typical 46 inch diameter drum. Typically, in the prior art, they are not described as being specifically used for altering or otherwise modifying the air flow through the pad. Problems typically encountered in the aforesaid configuration are uneven fiber density in the pad, especially at the ends, and clumping due to scarfing of the pad by high velocity air tangent to the screen. This problem is primarily due to the wide spacing of the support struts which induces turbulence during the transition of the pad ends from a low pressure plenum to a higher pressure plenum.
It is well known in the patent art that in order to obtain high pad integrity it is necessary to have a high air flow through the pad during forming sequence. However, the large volume of air produces air turbulence and instability especially at the ends and edges of the forming pocket and, consequently, the fiber distribution problems described above occur. These instabilities are usually seen as eddies or pulsing at the extreme pad ends as the pocket ends transition into or from the low pressure source. Further, the sides of the pads are also disturbed by the development of local edge turbulence because the solid or non-foraminous pocket sides are not able to adequately vent the forming air.
Considerable investigation into the aerodynamics of the forming system indicated that, contrary to the current commercial practice of having the number of radial support struts minimized, a large and unexpected improvement in the density and uniformity of the whole pad and especially the pad ends and sides was produced by using airflow control louvers in place of supports and spacing the airflow control louvers at three radial degrees based on a the 46 inch inside diameter of the standard drum former.
It was also determined by experimentation that when the lateral cross section of the louver was modified such that lateral radial surface was made concave or convex in the lateral direction the resulting air flow was altered sufficiently to change the lateral cross sectional profile of the pad. Similar effects were noted when the lateral cross section of the louver was modified such that lateral radial surface was made concave or convex in the radial direction the resulting air flow was altered sufficiently to change the lateral cross sectional profile of the pad.
A further invention, which also contributes to a significant reduction in turbulence at the pocket ends, is the use of an innovative method of end rail design. This consists of tapering the end rails so that they do not disturb the air flow and present a more aerodynamic surface as compared to the typical blunt edge used in pad former supports. This design virtually eliminates turbulence caused by conventional step-edged rails.
A further invention was discovered by off-setting the sub-plate support system at its internal circumferential edges. This created an opening to permit the venting or passage of air along the vertical height of the forming pocket and reduced air turbulence to a minimum.
The current invention is aimed at a simple and cost effective means for forming uniform fluff pads with high pad integrity. This is advantageously applied to a drum-style former especially since the overall design of the modular pocket assembly permits the construction of a totally self-supporting outside drum with no side supports. This provides a unique capability to create a free standing and totally self-supporting drum assembly by use of modular pockets placed end-to-end and permits the easy adaptation of the system to competitive drum former suction internals and drive shaft assemblies. The self support system is accomplished by the use of a novel concentricity stabilizer which permits construction of the individual modular pocket assemblies into a perfectly circular drum ready for attachment to suitable drum flanges or discs and shaft assemblies for installation on virtually any pad forming line.
It should be recognized that the pad former pocket construction concept is not limited to drum formers but can be adapted to other former configurations including linear endless "belt" systems.
In evaluations of competitive equipment before modification with the modular pad former system it was determined that, in addition to the air turbulence problems detailed above, the pressure profile across the width of the drum below the inner diameter of the drum had significant variations due to problems with the internal low pressure side design. This resulted in variations in fiber density and the amount or weight of fiber per square inch across the pad width.
A further invention that eliminated this problem is a unique adjustable airflow control louver. This airflow control louver can modify air flow across the width of the modular pad former system. The adjustable side of the airflow control louver is rotatable around its hinge point thereby reducing or otherwise altering, in a controllable and desirable manner, the pattern of air flow between any two airflow control louvers. The airflow control louver is rotated until the required results are achieved and then locking it in place by a locking means. It was discovered that when the adjustable portion of the airflow control louver was modified such that its radial length diminished at a uniform rate across the width of the pad former in the correct conformity that the density and amount of fiber per square inch could be made uniform. Other adjustable airflow control louver profiles provide further control and modification of density and weight per square inch.
A further invention is the tilt lock screen strap system which provides a positive method for locking the ends of the inner and outer foraminous layers in place without tearing or damaging them. This consists of a hold down strap which fits into a horizontal slot milled into the outer surface of each end plate. The lower surface of the slot is further divided into two depths. The plate is clamped in place by a screw or other fastening device which penetrates the lower milled surface of the slot. The tilt lock strap or plate end farthest from the screen ends rests on the apical section of the slot which acts as a pivot point for the strap when the fastening means is tightened thus providing a leverage to the plate, which translates into a high linear locking pressure on the screens at their outer ends.